Mobile communications systems typically consist of a mobile switching centre connected to a number of basestation controllers, each basestation controller controlling a number of basestation transceivers each located in a respective cell. A first connection can be established between a mobile station located in a particular cell and the mobile switching centre by establishing a traffic channel (RF link) between the basestation transceiver in the particular cell, and a corresponding channel from the basestation transceiver through the relevant basestation controller to the mobile switching centre. A call between a mobile terminal and a second terminal (which may be a wireless terminal, a wireline terminal, or an inter-mobile switching centre agent for example) is connected when a second connection from the mobile switching centre to the second terminal is made, and the first and second connections are bridged.
In the normal course of events, a traffic channel is assigned through a traffic channel assignment procedure and then communications over the assigned traffic channel commence. This "normal course of events" includes handoff, conversation mode, mobile origination and mobile termination scenarios. In a handoff, a traffic channel assignment is sent and the mobile starts communicating with a new basestation over a new traffic channel. In conversation mode the mobile simply continues to communicate over the assigned channel. In a mobile origination, a traffic channel is assigned as a result of a user of the mobile originating a call and then communications over the traffic channel commence. In a mobile termination, a traffic channel is assigned as a result of another party making a call to the mobile terminal, and then communications over the assigned traffic channel commence.
In any of the above scenarios, the traffic channel may be lost after the successful completion of the traffic channel assignment. This may be due to failure to connect to the newly assigned traffic channel as in the case of a handoff, mobile origination or mobile termination, or simply due to the failure to maintain communications over the traffic channel after it has been connected. In existing systems, when a traffic channel is dropped in any of the above-identified circumstances, the entire call is torn down meaning that the second connection to the second terminal is also disconnected, and either the caller or the callee must redial the other party's number to be reconnected.
One problem with this situation is that dropped calls and connect failures are annoying to customers. More importantly, any time that a call is dropped or fails to be connected, there exists the possibility that the parties involved will not bother to attempt to reconnect, and this represents lost revenue to the operating companies.
Another drawback with dropped calls is that some of them may be emergency calls such as 911 calls and a person making such a call may not have the opportunity to attempt it again should the call be dropped.